Quota delete command doesn't reset quota to default values

According to
http://docs.openstack.org/user-guide-admin/networking_advanced_quotas.html,
when you run the quota-delete command, "you can see that quota
values for the tenant are reset to the default values". However,
this is not the current behavior of the neutron plugin which
resets quotas to value -1 (unlimited quota).

1. We update the network quota value
    $ neutron quota-update --tenant-id ea6c9e9d64684449af1ac298e60d68f0 --network 42 -c network -f json
    [{"Field": "network", "Value": 42}]
2. We delete quotas associated to tenant ea6c9e9d64684449af1ac298e60d68f0w
    $ neutron quota-delete --tenant-id ea6c9e9d64684449af1ac298e60d68f0w
    Deleted quota: ea6c9e9d64684449af1ac298e60d68f0
3. Quota default value defined in /etc/neutron.conf
    $ grep quota_network /etc/neutron/neutron.conf
    quota_network = 10
4. But after deletion, the quota is set to -1
    $ neutron quota-show --tenant-id ea6c9e9d64684449af1ac298e60d68f0 -c network -f json
    [{"Field": "network", "Value": -1}]

However, the valid result is [{"Field": "network", "Value": 10}].